Difference between revisions of "Fire" - New World Encyclopedia

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Fire is one of the most intriguing phenomena in nature. When a fire rages out of control, it can be very destructive, damaging property and claiming lives. But humans have learned to tame fire and use it as a tool for the development of civilization. This ability, along with other talents, sets us apart from the animal world. Today we use fire to cook food, heat our homes, run engines, and drive industrial processes and power plants. Unfortunately, people have also used fire for destructive purposes, as in cases of arson and warfare.
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[[Image:Large bonfire.jpg|thumb|300px|A large [[bonfire]].]]
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'''Fire''' occupies a unique place in nature. It is not matter itself, but it involves the reaction of different types of matter to generate energy in the form of heat and light. It can be an agent of destruction, especially when uncontrolled, but it also serves many beneficial functions. In early [[geology|geological]] history, it appears that fires started by lightning strikes and volcanic eruptions shaped the [[Earth]] and helped prepare the environment for habitation by a huge diversity of life forms. Even today, periodic forest fires and brush fires are part of nature's cycle of destruction and renewal.
  
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In addition, fire has played an important role in the development of philosophical and religious thought. For instance, ancient philosophers in various cultures considered fire as one of the fundamental "elements" of nature. Religious thinkers have taken the heat and light of fire as metaphors for God's love and truth, respectively.
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Human beings, among all the species on Earth, have the unique ability to control fire. Based on this ability, fire has played an enormous role in the development of human civilization. Human scientific and technological advances, as well as their everyday lives, depend on the controlled use of fire. Fire is used to cook food, heat homes, run engines, smelt metals, generate electricity, and drive all manner of industrial processes.
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{{toc}}
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[[Image:Large bonfire.jpg|thumb|300px|A large [[bonfire]]]]
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Ancient philosophers considered fire as one of the fundamental "elements" of nature, while religious thinkers regarded the heat and light of fire as metaphors for God's love and truth, respectively. A flickering flame is a thing of beauty and endless fascination.
  
 
==What is fire?==
 
==What is fire?==
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[[Image:Log in fireplace.jpg|thumb|250px|Log burning in fireplace.]]
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When we see a piece of [[wood]] burning, with flames leaping and smoke rising, we say that the wood is "on fire." But what is fire? In general terms, fire is a high-temperature [[chemical reaction]] in which a [[fuel]] rapidly reacts with an oxidizing agent to generate [[heat]], [[light]], and a variety of products. In other words, fire is not matter itself, but it is the interaction of some forms of matter (such as [[hydrocarbon]]s and [[oxygen]]) at a relatively high temperature to generate other forms of matter (such as [[carbon dioxide]] and [[water]]) and energy (heat and light).
  
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When we see a piece of [[wood]] burning, with flames leaping and smoke rising, we say that the wood is "on fire." But what is fire? In general terms, fire is a [[chemical reaction]] in which a [[fuel]] rapidly reacts with an oxidizing agent to generate [[heat]], [[light]], and a variety of products. The [[fuel]] may be a [[solid]] (such as wood or paper), a [[liquid]] (such as oil or gasoline), or a [[gas]] (such as hydrogen or natural gas).
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The fuel may be a [[solid]] (such as wood or [[paper]]), a [[liquid]] (such as [[oil]] or [[gasoline]]), or a [[gas]] (such as [[hydrogen]] or [[natural gas]]). The oxidizing agent is usually [[oxygen]]. Gasoline and natural gas are mainly composed of hydrocarbon molecules, while wood and paper contain long-chain [[carbohydrate]]s (such as [[cellulose]]). When these fuels are burned in oxygen, the main products are carbon dioxide, water vapor, and [[carbon]] particles. If the fuel contains [[nitrogen]] and [[sulfur]], [[oxide]]s of these [[element]]s are produced as well.
  
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The oxidizing agent is usually [[oxygen]], but it could also be [[chlorine]] or [[fluorine]]. For instance, [[hydrogen]] can burn in [[chlorine]] to produce [[hydrogen chloride]] (HCl). Other possible combinations that produce flames include [[hydrogen]] and [[fluorine]] or [[hydrazine]] and [[nitrogen tetroxide]].
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Some fires occur in the absence of oxygen. For instance, [[hydrogen]] can burn in [[chlorine]] to produce [[hydrogen chloride]] (HCl). Other possible combinations that produce flames include hydrogen and [[fluorine]] or [[hydrazine]] and [[nitrogen tetroxide]].
  
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To start a fire, the [[fuel]] usually needs to be heated until it reaches a temperature known as its ''ignition point.'' At that temperature, some of the [[fuel]] is converted to flammable gases, which then react with the surrounding oxygen gas. Once started, the fire usually generates sufficient heat to sustain itself until the available fuel or oxygen is used up. But if the heat generated by combustion does not keep the temperature at or above the ignition point, the fire will die out.
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It takes a spark to start a fire. In scientific terms, the fuel—when surrounded by the oxidizing agent—needs to be heated until it reaches a temperature known as its ''ignition point.'' While it may seem like a handicap to someone trying to start a fire without a source for a spark, this requirement has a protective effect, considering how dangerous it would be if most fuels could burst into flames simply by being exposed to air at ordinary temperatures. (Some extremely flammable fuels have a low ignition temperature and are therefore stored in air-tight containers away from oxygen.)
  
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Many fuels, such as gasoline and paraffin wax, are mainly composed of [[hydrocarbon]] molecules, which contain [[carbon]] and [[hydrogen]] atoms. Others, such as [[wood]], contain large [[carbohydrate]] molecules (such as cellulose) that in turn are made up of [[carbon]], [[hydrogen]], and [[oxygen]] atoms. When these fuels are burned, the products include [[carbon dioxide]], [[water]] vapor, and [[carbon]] particles.
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At the ignition temperature, some of the fuel is converted to flammable gases, which then react with the surrounding oxygen gas. Once started, the fire usually generates sufficient heat to sustain itself until the available fuel or oxygen is used up. But if the heat generated by combustion does not keep the temperature at or above the ignition point, the fire will die out.
  
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==The flame==
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Some chemicals called ''accelerants'' can be used to spread fire faster or have it burn hotter. Common accelerants are hydrocarbon-based fuels, including gasoline, [[diesel]] fuel, [[kerosene]], [[turpentine]], and [[butane]].
  
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The flame consists of gases, solid particles, [[heat]], and [[light]]. The bright red-orange color of a flame is attributable to the presence of solid particles (mainly [[carbon]]) that have been heated to incandescence. These solid particles also form the [[soot]] emitted by the fire. In addition, the gas molecules in a flame have some of their electrons in "excited" (relatively high) energy states, and when these electrons return to lower energy levels, the molecules emit some light.
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To put out a fire, one has to do at least one of two things: (1) Cool the reacting matter until the temperature falls below the ignition point, or (2) prevent the oxygen (or other oxidizing agent) from contacting the fuel. Cooling the reaction is usually accomplished by pouring cold water on the burning matter. Alternatively, one can use a [[fire extinguisher]] to spray nonflammable material onto the fuel, thereby smothering the fuel and cutting off the oxygen supply. A third alternative—removing the fuel from the site of combustion—is usually not practical, as the fuel may be too hot or difficult to move.
  
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[[Image:flame.inflates.balloon.bath.arp.jpg|left|thumb|"A large flame is seen while firing the propane burners during inflation of a [[hot air balloon]]]]
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==The flame==
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The flame consists of gases, solid particles, [[heat]], and [[light]]. The bright red-orange color of a flame is attributable to the presence of solid particles (mainly [[carbon]]) that have been heated to incandescence. These solid particles form the [[soot]] emitted by the fire. The flame also derives part of its light from gas molecules, when some of their electrons undergo transitions from higher to lower energy levels.
  
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The color of the flame depends on its chemical composition, the temperature of combustion, and the extent of combustion of the fuel. Take the example of a [[Bunsen burner]] that burns [[methane]] gas, using oxygen from the air. If we restrict the amount of oxygen that mixes with the gas, the combustion is incomplete and we get a yellow flame at roughly 1,000 C. As additional oxygen is allowed to mix in, the extent of combustion increases, and the flame turns increasingly blue. The blue part of the flame is around 1,600 C. By comparison, the flame temperature of a [[blowlamp]] can be 1,300 C and that of a [[candle]] can reach 1,400 C. An [[oxyacetylene]] combustion can be as hot as 3,000 C.
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[[Image:flame.inflates.balloon.bath.arp.jpg|left|250px|thumb|A large flame from propane burners is used to inflate a hot air balloon.]]
  
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Generally speaking, a red flame is relatively cool. As the flame's temperature increases, its color turns to orange, yellow, white, violet and blue, and bright blue. For a given region of a flame, the closer it gets to white, blue, or bright blue, the hotter that region is.
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The color of the flame depends on its chemical composition, the temperature of combustion, and the extent of combustion of the fuel. Take the example of a [[Bunsen burner]] that burns [[methane]] gas, using oxygen from the air. If we restrict the amount of oxygen that mixes with the gas, the combustion is incomplete and produces a yellow flame at roughly 1,000°C. As additional oxygen is allowed to mix in, the extent of combustion increases, and the flame turns increasingly blue. The blue part of the flame is around 1,600°C. By comparison, the flame temperature of a blowlamp can be 1,300°C and that of a [[candle]] can reach 1,400°C. An [[oxyacetylene]] combustion can be as hot as 3,000°C.
  
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In addition, when salts of different metals are heated in the flame of a Bunsen burner, they produce specific colors in the flame. For instance, sodium salts produce a yellow flame, potassium salts give a violet color, and copper salts make the flame green or blue-green.
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Generally speaking, a red flame is relatively cool. As the flame's temperature increases, its color turns to orange, yellow, white, violet, blue, and bright blue. For a given region of a flame, the closer it gets to white, blue, or bright blue, the hotter that region is.
  
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==Uses of controlled fire==
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In addition, when salts of different metals are heated in the flame of a Bunsen burner, they produce specific colors in the flame. For instance, sodium salts produce a yellow flame, potassium salts give a violet color, and copper salts make the flame green or blue green.
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[[Image:Log in fireplace.jpg|thumb|250px|Log in fireplace]]
 
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[[image:Gas burner on stove.jpg|thumb|right|125px|Small open fire]]
 
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Controlling fire and using it to provide [[heat]] and [[light]] was one of [[human]]kind's first great achievements. Studies in [[archaeology]] indicate that the hominid species ''[[Homo erectus]]'' may have been using controlled fire as early as 790,000 years ago. Evidence from the site named the "Cradle of Humankind" in South Africa suggests the controlled use of fire more than a million years ago.
 
  
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The ability to use fire to generate heat enabled people to [[cooking|cook]] food—a decisive step in the fight against [[disease]]—and to migrate to colder climates. Before the advent of electricity, people relied on fire as a means of lighting dark places. Another use of fire was in long-distance communication through [[smoke signals]]. In addition, fire enabled advances in [[metallurgy]], such as [[smelting]] and [[forging]].
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==Usefulness of controlled fire==
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{{readout|Learning to control fire was one of the first great achievements of [[hominid]]s.|left}} Some paleontologists indicate that ''[[Homo erectus]]'' may have used controlled fire as early as 790,000 years ago. Other evidence from the site named the "Cradle of Humankind" in [[South Africa]] suggests the controlled use of fire more than a million years ago. But reliable means of starting a fire—such as by the use of wooden drills or flintstones—has been traced to the [[Neolithic period|Neolithic age]], around 7000 B.C.E.
  
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By the time of the Neolithic introduction of grain-based agriculture, people the world over used fire as a tool in landscape management. These were typically controlled, "cool fires" conducted in the spring or fall in order to improve the yield of root and berry crops by clearing undergrowth, to drive game, to provide a greater variety of environments that encouraged plant and game diversity in the fresh grass in burnt off prairies and corridors
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For early peoples, wood fires were a main source of energy. The ability to control fire enabled them to [[cooking|cook]] food—a decisive step in the fight against [[disease]]—and to migrate to colder regions of the world. Controlled flames also offered a means of lighting dark places. Another use of fire was in long-distance communication through smoke signals.
  
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that contrasted with unburnt forest patches that were often deliberately protected, to produce prairie, savannah and meadow landscapes that facilitated travel and overall human utility compared to impenetrable jungles and forests and, to prevent, once the biomass builds up with no fires, unplanned "hot fires" which damage the soil. Such hot fires destroy plants and animals, and endanger communities. All too often this is a problem in the forests of today where traditional burning is prevented in order to encourage the growth of timber crops.  
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By the time of the Neolithic introduction of grain-based agriculture, people the world over used fire as a means to clear fields, produce fertilizer (by burning trees and grasses), and manage landscapes. For instance, controlled fires helped clear the undergrowth in forested areas, thereby facilitating hunting and improving the yield of root and berry crops. Fire was also used to clear travel lanes.
  
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Today, the applications of fire are numerous. Beyond its use as an energy source in engines and power plants, fire is used for such varied purposes as [[incinerating]] waste, [[smoking]], and as a [[weapon]].
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[[Image:Blacksmiths fire.jpg|thumb|right|250px|A blacksmith's fire, used primarily for forging [[iron]].]]
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Later, fire enabled advances in [[metallurgy]], such as smelting and forging, and alchemists used fire to discover and perform a variety of chemical reactions. That type of work contributed to the foundations of our modern technological society. Today, the energy needs for modern homes, offices, industries, agriculture, and means of transportation rely, for the most part, on the burning of fuel, either directly or indirectly.
  
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In fact, the use of fire by militaries has a long history. [[Homer]] detailed its use by Greek [[commando|commandoes]] who hid in a [[Trojan Horse|wooden horse]] to burn [[Troy]] during the [[Trojan war]].
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When people use electricity, fuel is not burned on site, but most of the world's electricity is generated by power stations that burn [[coal]], [[oil]], or [[natural gas]]. At a [[power station]], fire is used to heat water, creating steam that drives [[turbine]]s. The turbines are linked to an [[electrical generator]]. In most developing countries and remote areas, however, wood continues to be the primary energy source.
  
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[[Greek Fire]] and its modern contemporary [[napalm]] are chemical solutions that are burned to disable, kill, or destroy infrastructure.
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There is also a long history of the use of fire in warfare. [[Homer]] detailed its use by Greek commandos who hid in a wooden horse to enter [[Troy]] and burn the city during the [[Trojan War]]. A more recent example is the use of [[napalm]], consisting of gasoline jelled in aluminum soaps, to kill and maim people and destroy infrastructure.
  
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==Fire in philosophy and religion==
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==Uncontrolled fire==
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Fires and burning have often been used in [[religion|religious]] rites and symbolism, as the [[smoke]] of the fire disperses into the heavens. Fire is one of the four [[classical element]]s, as well as one of the [[Five elements|five Chinese elements]]. In [[Hinduism]] fire is one of five sacred elements of which all living creatures are comprised and is considered an eternal witness essential to sacred religious ceremonies. In [[Christianity]], fire is a [[symbol]] of the [[Holy Ghost]] and is often used in descriptions of [[Hell]]. Fire is a symbol of [[Ahura Mazda]], or God, of the [[Zoroastrian]] religion. A Zoroastrian church is known as a [[Agiary|Fire Temple]]. Fire is also an important part of [[Calcinatio]], the fire operation in the art of [[alchemy]]. In Greek mythology, [[Prometheus]] is the [[Titan]] chiefly honored for stealing fire from the gods in the stalk of a fennel plant and giving it to mortals for their use. In [[Judaism]] fire also has great significance, candles are lit to usher in holidays and to seperate [[Shabbat]] from the rest of the week, as well as to remember the dead; another important fire symbol is the Eternal Flame, which was a fire kept in the First and Second Temple was never supposed to go out.
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Uncontrolled fires are extremely dangerous, as they spread swiftly, destroy property, and kill and injure living things.  
  
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==Fire as a power source==
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Naturally occurring wildfires consume huge areas of forests and grasslands. In the long run, however, these fires also have certain beneficial effects. They thin out forests, free up nutrients from wood, and encourage vegetation that depends on regular burns for survival. Knowing the role of fire in ecosystems, forest rangers may use "prescribed burns" to reduce the hazards of undergrowth and dead fuels.  
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Fire has supplied much of the energy which has helped humans since ancient times, from the wood fires which served many prehistoric purposes to the oil, gas and coal power stations of today which supplies the vast majority of the world's electricity (nearly 80%<sup>1</sup>). Mexico is typical with thermal energy providing 76% of all energy<sup>2</sup>.
 
  
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The burning of [[wood]] is often the first association to the word "fire". It is common in a [[developing countries|developing country]] for wood to be the primary energy source as well. For instance, in [[Africa]], 65% of the energy used comes from the burning of [[biomass]]<sup>3</sup>. What is less obvious is that wood burning power stations are less environmentally destructive than the fired oil power station in two major respects. E.ON UK is soon to build a 44 megawatt wood fired power station in [[Britain]] for these reasons, as reported in the [[The Guardian|Guardian]] newspaper in October 2005<sup>4</sup>: first, wood is a renewable resource, especially if trees are grown in a modern, sustainable way. Second, the [[carbon dioxide]] emissions are negligible because no more carbon dioxide can be produced by burning than would be produced by the natural rotting of wood. Thus, over a 100-year timescale, the effect is carbon-neutral<sup>5</sup>. It is also claimed that this power station will be more efficient than coal: [[Accelerant|accelerants]] can be used to spread fire faster or have it burn hotter.
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In day-to-day human lives, structure fires can be started by [[cooking]] accidents, [[electricity|electrical]] faults, fuel leaks, children playing with lighters or matches, and accidents involving [[candle]]s and [[cigarette]]s. Fire can propagate rapidly to neighboring structures, especially when proper [[building standards]] are not met. Purposefully starting destructive fires constitutes [[arson]] and is a criminal offense in most jurisdictions.
  
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The fire in a [[power station]] is used to heat water, creating steam that drives [[Turbine|turbines]]. The turbines are linked to an [[electrical generator]].
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Given the destructive capacity of fire, most [[municipality|municipalities]] offer [[firefighting]] services to quickly extinguish fires. Trained [[firefighter]]s use [[fire truck]]s, [[fire hydrant]]s, and an array of other equipment to combat the spread of fires.
  
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The burning of [[wood]] is often the first association to the word ''fire'', and [[tree]]s have supplied much of the energy needed by humans since ancient times, and early applications of fire consumed large amounts of wood. Since the [[Industrial Revolution]], [[hydrocarbon]] [[petroleum]] and [[coal]] has become a preferred fuel. Wood burning remains a heat source in many [[Third world]] countries and remote areas where other sources of energy are unavailable, often leading to [[deforestation]]. [[Accelerant|Accelerants]] can be used to spread fire faster or have it burn hotter.
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Uncontrolled fires have been classified according to different systems. In the [[United States]], they are classified into four groups, as follows.
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* Class A: Fires that involve flammable [[solid]]s such as [[wood]], [[cloth]], [[rubber]], [[paper]], and some types of [[plastic]]s.
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* Class B: Fires that involve [[grease]]s, flammable liquids (including [[gasoline]], [[oil]], and [[paint]]), and flammable gases (such as [[natural gas]] and [[propane]]).
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* Class C: Fires that involve any of the materials found in Classes A and B, but with the presence of any electrical appliances, wiring, or other electrically energized objects in the vicinity of the fires.
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* Class D: Fires that involve [[combustion|combustible]] [[metal]]s, such as [[sodium]], [[magnesium]], and [[potassium]].
  
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==Uncontrolled fire==
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Occasionally, a fifth group, Class K, is added. It refers to fires involving large amounts of grease or oil. Although Class K is a subclass of Class B, the special characteristics of these types of fires are considered important enough to recognize.
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[[Image:Wohnhausbrand.JPG|thumb|230px|left|A [[house]] on fire]]
 
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The self-sustaining nature of fire makes it extremely dangerous if uncontrolled. Fire can consume structures and forests and can severely injure living things through [[burn]]s or [[smoke inhalation]]. Structure fires can be started by [[cooking]] accidents, [[electricity|electrical]] faults, [[fuel]] leaks, children playing with lighters and/or matches, and accidents involving [[candle]]s and [[cigarette]]s. Fire can propagate rapidly to other structures, especially where proper [[building standards]] are not met. Purposefully starting destructive fires constitutes [[arson]] and is a criminal offense in most jurisdictions. The destructive capacity of fire has led most [[municipality|municipalities]] to offer [[fire fighting]] services to quickly extinguish fires; Trained [[firefighter]]s use [[fire truck]]s, [[fire hydrant]]s, and an array of other equipment to combat the spread of fires. Outside of urban settings, [[wildfire]]s can consume large areas of [[forest]] and brush and often damage nearby settlements.
 
  
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There are many different classification systems used for uncontrolled fires; In [[Europe]] and [[Australasia]] 6 groups are used:
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[[Image:Forestfire2.jpg|thumb|right|250px|A forest fire]]
  
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* Class A: Fires that involve flammable [[solid]]s such as [[wood]], [[cloth]], [[rubber]], [[paper]], and some types of [[plastic]]s.
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In [[Europe]] and [[Australasia]], six groups are used:
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* Class B: Fires that involve flammable [[liquid]]s or liquefiable solids such as [[gasoline|petrol/gasoline]], [[oil]], [[paint]], some [[wax]]es & plastics, but NOT cooking fats or oils.
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* Class A: Fires that involve flammable solids such as wood, cloth, rubber, paper, and some types of plastics.
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* Class C: Fires that involve flammable [[gas]]es, such as [[natural gas]], [[hydrogen]], [[propane]], [[butane]]
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* Class B: Fires that involve flammable liquids or liquefiable solids such as [[gasoline|gasoline/petrol]], oil, paint, some [[wax]]es and plastics, but not cooking fats or oils.
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* Class D: Fires that involve [[combustion|combustible]] [[metal]]s, such as [[sodium]], [[magnesium]], and [[potassium]].
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* Class C: Fires that involve flammable gases, such as natural gas, hydrogen, propane, and butane.
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* Shock Risk (formerly known as Class E): Fires that involve any of the materials found in Class A and B fires, but with the introduction of an electrical appliances, wiring, or other electrically energized objects in the vicinity of the fire, with a resultant electrical shock risk if a [[electrical conduction|conductive]] agent is used to control the fire.
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* Class D: Fires that involve combustible metals, such as sodium, magnesium, and potassium.
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* Class F: Fires involving cooking fats and oils. The high temperature of the oils when on fire far exceeds that of other flammable liquids making normal extinguishing agents ineffective
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* Shock Risk (formerly known as Class E): Fires that involve any of the materials found in Classes A and B, but with the presence of any electrical appliances, wiring, or other electrically energized objects in the vicinity of the fires, with a resultant electrical shock risk if a [[electrical conduction|conductive]] agent is used to control the fire.
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* Class F: Fires involving cooking fats and oils. The high temperature of the oils when on fire far exceeds that of other flammable liquids making normal extinguishing agents ineffective.
  
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[[Image:Forestfire2.jpg|thumb|right|180px|A forest fire]]
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==Fire in philosophy and religion==
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In the [[United States|U.S.]], fires are generally classified into four groups: A, B, C, and D.
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In [[Greek mythology]], [[Prometheus]] was the [[Titan]] honored chiefly for stealing fire from the gods in the stalk of a fennel plant and giving it to mortals for their use. On a more mundane level, Greek philosopher [[Empedocles]] proposed, in the fifth century B.C.E., that fire was one of four unchanging elements that were the basic constituents of all material things. The other three elements he proposed were air, water, and earth. For the ancient Chinese, there were five basic elements: Fire, water, earth, metal, and wood. The modern concept of elements was not formulated until the seventeenth century, when [[Robert Boyle]] defined them as material substances that could not be broken down into simpler substances.
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* Class A: Fires that involve wood, cloth, rubber, paper, and some types of plastics.
 
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* Class B: Fires that involve gasoline, oil, paint, natural and propane gases, and flammable liquids, gases, and greases.
 
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* Class C: Fires that involve any of the materials found in Class A and B fires, but with the introduction of an electrical appliances, wiring, or other electrically energized objects in the vicinity of the fire.
 
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* Class D: Fires that involve combustible metals, such as sodium, magnesium, and potassium.
 
  
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A fifth group, Class K, is sometimes added. It refers to fires involving large amounts of grease or oil. Although, by definition, Class K is a subclass of Class B, the special characteristics of these types of fires are considered important enough to recognize.
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Fire also plays an important role in the symbolism and rituals of many religions. For instance, candles and oil lamps are often used in places of meditation and prayer. Just as light dispels darkness, the light of a flame has been taken as a metaphor for goodness that dispels the darkness of evil. In addition, the heat and light of fire may be seen as metaphors for God's love and truth, and the upward movement of the flame may be seen as pointing toward a higher realm.
  
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[[Image:Blacksmiths fire.jpg|thumb|250px|A [[blacksmith]]'s fire, used primarily for [[forging]] [[iron]].]]
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In [[Hinduism]], fire is regarded as one of five sacred elements that make up all living creatures and as an eternal witness essential to sacred ceremonies. The [[Zoroastrianism|Zoroastrian]] religion considers fire as a symbol of the invisible God, or [[Ahura Mazda]], and each temple—called a [[fire temple]]—maintains a holy flame. In [[Judaism]], believers light candles to usher in holidays, separate [[Shabbat]] from the rest of the week, and remember the dead. The Jews also had the tradition of maintaining an Eternal Flame in the First and Second Temple.
  
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==See also==
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[[Christianity|Christians]] regard fire as a symbol of the [[Holy Spirit]], but they also point to biblical verses that prophesy a time when the world will be judged by fire (2 Peter 3:12; Malachi 4:1). [[Jesus]] is recorded as saying that he came to "cast fire upon the earth" (Luke 12:49). Many Christians regard these words about judgment by fire as symbolic, and not to be taken literally. The prophet [[Jeremiah]] likened fire to God's word (Jeremiah 23:29), hence "judgment by fire" can be a metaphor for judgment by God's truth.
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* [[Backdraft]]
 
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* [[Bonfire]]
 
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* [[Bushfire]]
 
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* [[Campfire]]
 
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* [[Combustion]]
 
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* [[Explosion]] - another form of combustion/oxidation
 
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* [[Fire drill]]
 
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* [[Fire eater]]
 
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* [[Fire hydrant]]
 
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* [[Fire point]]
 
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* [[Fire-retardant material]]
 
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* [[Firestorm]]
 
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* [[Firewall (construction)|Firewall]]
 
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* [[Flash point]]
 
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* [[Flashover]]
 
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* [[Flint and steel fire]]
 
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* [[Immolation]]
 
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* [[List of historic fires]]
 
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* [[Reckless burning]]
 
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* [[Rust]] - another form of combustion/oxidation
 
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* [[Trench effect]]
 
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* [[Wildfire]], also known as a '''forest fire'''
 
  
 
==References==
 
==References==
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*[http://www.iea.org/statlist/index.htm "Share of Total Primary Energy Supply", 2002; International Energy Agency]
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*Pyne, Stephen J. ''World Fire: The Culture of Fire on Earth''. University of Washington Press, 1997. ISBN 978-0295975931
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*[http://www.geni.org/globalenergy/library/national_energy_grid/mexico/index.shtml  "Mexico Grid Summary", 2000; Global Energy Network Institute]; thermal energy defined as oil, gas and coal
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*Pyne, Stephen J. ''Fire: A Brief History''. University of Washington Press, 2001. ISBN 978-0295981444
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*[http://www.eia.doe.gov/emeu/cabs/archives/africa/chapter3.html "Energy in Africa - Chapter 3"], US Energy information administration
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*Pyne, Stephen J. ''Between Two Fires: A Fire History of Contemporary America''. University of Arizona Press, 2015. ISBN 978-0816532148
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*[http://www.guardian.co.uk/science/story/0,3605,1592854,00.html "How Can Burning Wood Help Reduce Global Warming"], The Guardian
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*Ward, Michael J. ''Fire Officer: Principles and Practice''. Jones & Bartlett Learning, 2014. ISBN 978-1284068368
  
 
==External links==
 
==External links==
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All links retrieved March 26, 2024.
  
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{{commons|Fire}}
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* [http://www.hkc22.com/fireprotection.html Helmut Kaiser Consultancy Study: Fire Protection Industry Worldwide Innovation and Emerging Markets 2004–2010–2015]
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* ( http://www.hkc22.com/fireprotection.html ) Fire Protection worldwide for passive and active fireprotection 2005 to 2015
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* [http://news.bbc.co.uk/1/hi/sci/tech/3670017.stm "Early human fire skills revealed," BBC News]
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* [http://www.straightdope.com/columns/021122.html What exactly is fire?] (from [[The Straight Dope]])
 
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* [http://news.bbc.co.uk/1/hi/sci/tech/3670017.stm Early human fire mastery revealed] [[BBC]] article on archeological discoveries
 
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* [http://www.northmason.wednet.edu/NMHSonline/student_gallery/fire/pg19_candleflame.html Parts of a candle flame]
 
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* [http://microgravity.grc.nasa.gov/combustion/cfm/cfm_index.htm Flames in microgravity]
 
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* [http://science.nasa.gov/headlines/y2000/ast12may_1.htm Spiral flames in microgravity]
 
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* [http://www.moebuildingcontrol.co.uk moebuildingcontrol.co.uk - UK Guidance on fire safety codes and fire engineering]
 
  
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Latest revision as of 19:51, 26 March 2024

A large bonfire.

Fire occupies a unique place in nature. It is not matter itself, but it involves the reaction of different types of matter to generate energy in the form of heat and light. It can be an agent of destruction, especially when uncontrolled, but it also serves many beneficial functions. In early geological history, it appears that fires started by lightning strikes and volcanic eruptions shaped the Earth and helped prepare the environment for habitation by a huge diversity of life forms. Even today, periodic forest fires and brush fires are part of nature's cycle of destruction and renewal.

Human beings, among all the species on Earth, have the unique ability to control fire. Based on this ability, fire has played an enormous role in the development of human civilization. Human scientific and technological advances, as well as their everyday lives, depend on the controlled use of fire. Fire is used to cook food, heat homes, run engines, smelt metals, generate electricity, and drive all manner of industrial processes.

Ancient philosophers considered fire as one of the fundamental "elements" of nature, while religious thinkers regarded the heat and light of fire as metaphors for God's love and truth, respectively. A flickering flame is a thing of beauty and endless fascination.

What is fire?

Log burning in fireplace.

When we see a piece of wood burning, with flames leaping and smoke rising, we say that the wood is "on fire." But what is fire? In general terms, fire is a high-temperature chemical reaction in which a fuel rapidly reacts with an oxidizing agent to generate heat, light, and a variety of products. In other words, fire is not matter itself, but it is the interaction of some forms of matter (such as hydrocarbons and oxygen) at a relatively high temperature to generate other forms of matter (such as carbon dioxide and water) and energy (heat and light).

The fuel may be a solid (such as wood or paper), a liquid (such as oil or gasoline), or a gas (such as hydrogen or natural gas). The oxidizing agent is usually oxygen. Gasoline and natural gas are mainly composed of hydrocarbon molecules, while wood and paper contain long-chain carbohydrates (such as cellulose). When these fuels are burned in oxygen, the main products are carbon dioxide, water vapor, and carbon particles. If the fuel contains nitrogen and sulfur, oxides of these elements are produced as well.

Some fires occur in the absence of oxygen. For instance, hydrogen can burn in chlorine to produce hydrogen chloride (HCl). Other possible combinations that produce flames include hydrogen and fluorine or hydrazine and nitrogen tetroxide.

It takes a spark to start a fire. In scientific terms, the fuel—when surrounded by the oxidizing agent—needs to be heated until it reaches a temperature known as its ignition point. While it may seem like a handicap to someone trying to start a fire without a source for a spark, this requirement has a protective effect, considering how dangerous it would be if most fuels could burst into flames simply by being exposed to air at ordinary temperatures. (Some extremely flammable fuels have a low ignition temperature and are therefore stored in air-tight containers away from oxygen.)

At the ignition temperature, some of the fuel is converted to flammable gases, which then react with the surrounding oxygen gas. Once started, the fire usually generates sufficient heat to sustain itself until the available fuel or oxygen is used up. But if the heat generated by combustion does not keep the temperature at or above the ignition point, the fire will die out.

Some chemicals called accelerants can be used to spread fire faster or have it burn hotter. Common accelerants are hydrocarbon-based fuels, including gasoline, diesel fuel, kerosene, turpentine, and butane.

To put out a fire, one has to do at least one of two things: (1) Cool the reacting matter until the temperature falls below the ignition point, or (2) prevent the oxygen (or other oxidizing agent) from contacting the fuel. Cooling the reaction is usually accomplished by pouring cold water on the burning matter. Alternatively, one can use a fire extinguisher to spray nonflammable material onto the fuel, thereby smothering the fuel and cutting off the oxygen supply. A third alternative—removing the fuel from the site of combustion—is usually not practical, as the fuel may be too hot or difficult to move.

The flame

The flame consists of gases, solid particles, heat, and light. The bright red-orange color of a flame is attributable to the presence of solid particles (mainly carbon) that have been heated to incandescence. These solid particles form the soot emitted by the fire. The flame also derives part of its light from gas molecules, when some of their electrons undergo transitions from higher to lower energy levels.

A large flame from propane burners is used to inflate a hot air balloon.

The color of the flame depends on its chemical composition, the temperature of combustion, and the extent of combustion of the fuel. Take the example of a Bunsen burner that burns methane gas, using oxygen from the air. If we restrict the amount of oxygen that mixes with the gas, the combustion is incomplete and produces a yellow flame at roughly 1,000°C. As additional oxygen is allowed to mix in, the extent of combustion increases, and the flame turns increasingly blue. The blue part of the flame is around 1,600°C. By comparison, the flame temperature of a blowlamp can be 1,300°C and that of a candle can reach 1,400°C. An oxyacetylene combustion can be as hot as 3,000°C.

Generally speaking, a red flame is relatively cool. As the flame's temperature increases, its color turns to orange, yellow, white, violet, blue, and bright blue. For a given region of a flame, the closer it gets to white, blue, or bright blue, the hotter that region is.

In addition, when salts of different metals are heated in the flame of a Bunsen burner, they produce specific colors in the flame. For instance, sodium salts produce a yellow flame, potassium salts give a violet color, and copper salts make the flame green or blue green.

Usefulness of controlled fire

Did you know?
Learning to control fire was one of the first great achievements of hominids.

Learning to control fire was one of the first great achievements of hominids. Some paleontologists indicate that Homo erectus may have used controlled fire as early as 790,000 years ago. Other evidence from the site named the "Cradle of Humankind" in South Africa suggests the controlled use of fire more than a million years ago. But reliable means of starting a fire—such as by the use of wooden drills or flintstones—has been traced to the Neolithic age, around 7000 B.C.E.

For early peoples, wood fires were a main source of energy. The ability to control fire enabled them to cook food—a decisive step in the fight against disease—and to migrate to colder regions of the world. Controlled flames also offered a means of lighting dark places. Another use of fire was in long-distance communication through smoke signals.

By the time of the Neolithic introduction of grain-based agriculture, people the world over used fire as a means to clear fields, produce fertilizer (by burning trees and grasses), and manage landscapes. For instance, controlled fires helped clear the undergrowth in forested areas, thereby facilitating hunting and improving the yield of root and berry crops. Fire was also used to clear travel lanes.

A blacksmith's fire, used primarily for forging iron.

Later, fire enabled advances in metallurgy, such as smelting and forging, and alchemists used fire to discover and perform a variety of chemical reactions. That type of work contributed to the foundations of our modern technological society. Today, the energy needs for modern homes, offices, industries, agriculture, and means of transportation rely, for the most part, on the burning of fuel, either directly or indirectly.

When people use electricity, fuel is not burned on site, but most of the world's electricity is generated by power stations that burn coal, oil, or natural gas. At a power station, fire is used to heat water, creating steam that drives turbines. The turbines are linked to an electrical generator. In most developing countries and remote areas, however, wood continues to be the primary energy source.

There is also a long history of the use of fire in warfare. Homer detailed its use by Greek commandos who hid in a wooden horse to enter Troy and burn the city during the Trojan War. A more recent example is the use of napalm, consisting of gasoline jelled in aluminum soaps, to kill and maim people and destroy infrastructure.

Uncontrolled fire

Uncontrolled fires are extremely dangerous, as they spread swiftly, destroy property, and kill and injure living things.

Naturally occurring wildfires consume huge areas of forests and grasslands. In the long run, however, these fires also have certain beneficial effects. They thin out forests, free up nutrients from wood, and encourage vegetation that depends on regular burns for survival. Knowing the role of fire in ecosystems, forest rangers may use "prescribed burns" to reduce the hazards of undergrowth and dead fuels.

In day-to-day human lives, structure fires can be started by cooking accidents, electrical faults, fuel leaks, children playing with lighters or matches, and accidents involving candles and cigarettes. Fire can propagate rapidly to neighboring structures, especially when proper building standards are not met. Purposefully starting destructive fires constitutes arson and is a criminal offense in most jurisdictions.

Given the destructive capacity of fire, most municipalities offer firefighting services to quickly extinguish fires. Trained firefighters use fire trucks, fire hydrants, and an array of other equipment to combat the spread of fires.

Uncontrolled fires have been classified according to different systems. In the United States, they are classified into four groups, as follows.

  • Class A: Fires that involve flammable solids such as wood, cloth, rubber, paper, and some types of plastics.
  • Class B: Fires that involve greases, flammable liquids (including gasoline, oil, and paint), and flammable gases (such as natural gas and propane).
  • Class C: Fires that involve any of the materials found in Classes A and B, but with the presence of any electrical appliances, wiring, or other electrically energized objects in the vicinity of the fires.
  • Class D: Fires that involve combustible metals, such as sodium, magnesium, and potassium.

Occasionally, a fifth group, Class K, is added. It refers to fires involving large amounts of grease or oil. Although Class K is a subclass of Class B, the special characteristics of these types of fires are considered important enough to recognize.

A forest fire

In Europe and Australasia, six groups are used:

  • Class A: Fires that involve flammable solids such as wood, cloth, rubber, paper, and some types of plastics.
  • Class B: Fires that involve flammable liquids or liquefiable solids such as gasoline/petrol, oil, paint, some waxes and plastics, but not cooking fats or oils.
  • Class C: Fires that involve flammable gases, such as natural gas, hydrogen, propane, and butane.
  • Class D: Fires that involve combustible metals, such as sodium, magnesium, and potassium.
  • Shock Risk (formerly known as Class E): Fires that involve any of the materials found in Classes A and B, but with the presence of any electrical appliances, wiring, or other electrically energized objects in the vicinity of the fires, with a resultant electrical shock risk if a conductive agent is used to control the fire.
  • Class F: Fires involving cooking fats and oils. The high temperature of the oils when on fire far exceeds that of other flammable liquids making normal extinguishing agents ineffective.

Fire in philosophy and religion

In Greek mythology, Prometheus was the Titan honored chiefly for stealing fire from the gods in the stalk of a fennel plant and giving it to mortals for their use. On a more mundane level, Greek philosopher Empedocles proposed, in the fifth century B.C.E., that fire was one of four unchanging elements that were the basic constituents of all material things. The other three elements he proposed were air, water, and earth. For the ancient Chinese, there were five basic elements: Fire, water, earth, metal, and wood. The modern concept of elements was not formulated until the seventeenth century, when Robert Boyle defined them as material substances that could not be broken down into simpler substances.

Fire also plays an important role in the symbolism and rituals of many religions. For instance, candles and oil lamps are often used in places of meditation and prayer. Just as light dispels darkness, the light of a flame has been taken as a metaphor for goodness that dispels the darkness of evil. In addition, the heat and light of fire may be seen as metaphors for God's love and truth, and the upward movement of the flame may be seen as pointing toward a higher realm.

In Hinduism, fire is regarded as one of five sacred elements that make up all living creatures and as an eternal witness essential to sacred ceremonies. The Zoroastrian religion considers fire as a symbol of the invisible God, or Ahura Mazda, and each temple—called a fire temple—maintains a holy flame. In Judaism, believers light candles to usher in holidays, separate Shabbat from the rest of the week, and remember the dead. The Jews also had the tradition of maintaining an Eternal Flame in the First and Second Temple.

Christians regard fire as a symbol of the Holy Spirit, but they also point to biblical verses that prophesy a time when the world will be judged by fire (2 Peter 3:12; Malachi 4:1). Jesus is recorded as saying that he came to "cast fire upon the earth" (Luke 12:49). Many Christians regard these words about judgment by fire as symbolic, and not to be taken literally. The prophet Jeremiah likened fire to God's word (Jeremiah 23:29), hence "judgment by fire" can be a metaphor for judgment by God's truth.

References
ISBN links support NWE through referral fees

  • Pyne, Stephen J. World Fire: The Culture of Fire on Earth. University of Washington Press, 1997. ISBN 978-0295975931
  • Pyne, Stephen J. Fire: A Brief History. University of Washington Press, 2001. ISBN 978-0295981444
  • Pyne, Stephen J. Between Two Fires: A Fire History of Contemporary America. University of Arizona Press, 2015. ISBN 978-0816532148
  • Ward, Michael J. Fire Officer: Principles and Practice. Jones & Bartlett Learning, 2014. ISBN 978-1284068368

External links

All links retrieved March 26, 2024.

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